Glad I could help!
With the nails, it depends on how fast they grow and....how much damage you're willing for your furniture to take
I trim my two active kittens nails at least once a week (they're ~18 months old and do a nascar impression on top of the couch, etc). My older cat (~5 years and very inactive) can wait up to 2 weeks between trimmings, but I trim his once a week just so that he doesn't have an advantage on the kittens (he can be somewhat of a bully).
If he's not used to having them done, you may want someone to hold him and you trim the nails. Just take a little off at first and maybe just do 1 or 2 nails or just a foot and reward him afterwards... If he doesn't like having them done, this will hopefully teach him that nail trimming is a "good" thing.
BTW, I'd suggest a scissor-style nail clipper rather than the "guillotine" type (where you put the cat's nail in the hold and squeeze it shut to cut off the nail). I am using this one: http://www.amazon.com/Millers-Forge-...548431&sr=1-21
and have been happy with it.
As to the dry food = healthy teeth... I had always heard that too, but, as some on here have pointed out...does eating cereal help our teeth? My cats tend to either swallow dry food whole or crunch it (on the tips of their teeth) then swallow. It doesn't do much good for he sides of their teeth... I've read in posts before on here that some people think that wet food increases saliva and bacteria production, which helps keep their teeth clean... Not sure about that though. Also, many folks have had health problems result from feeding all dry (some people believe cats on all dry are basically always dehydrated because they get most of their food from their prey in the wild, so don't drink a lot). I know that a both cats that I had when I was growing up were fed all dry and both died from kidney / urinary problems.
One of my cats is prone to UTIs, so I've been trying to encourage mine to drink more (even bought a fountain) and I've been trying to feed more wet food. Now mine eat about 50/50 wet and dry and I haven't seen any ill effects on their teeth. If only I could convince them that the wet food was as yummy as the dry...
Whether it helps their teeth or not, I think that adding wet is a good idea just for variety's sake...That is, if your cat likes it. If you do decide to add some in, just try to avoid the cans with fish in them (especially if your cat is a male) as fish tends to increase the odds of a male cat developing crystals in his urine and having UTIs.
BTW, some vets, at leat in my experience, unless they specialize in nutrition, etc., tend to be somewhat undereducated in terms of pet diet, etc...they pretty much go by what the pet food companies tell them.. At least, my vet pulled out a science diet guidebook when I asked her a diet question about one of my cats who was overweight.
Good luck with your cat and let us know if we can help!